The present invention relates generally to laser-based pipe alignment systems which use a reference beam of light along a predetermined path to position sections of pipe and, more particularly, to a pipe alignment device which provides an air flow in the sections of pipe sufficient to reduce deflection of the reference beam of light caused by thermal stratification of the air in the pipe.
Reference laser beam systems have been employed in a number of surveying and construction applications. Laser beam systems have been used, for example, to great advantage in laying sections of pipe, such as sewer pipes. A laser beam transmitter provides a stationary laser beam which passes through the previously positioned sections along a central axis and establishes a reference line of light. A laser beam target having reference indicia thereon is placed in one end of a section of pipe to assist workers in positioning the section. The end of the pipe opposite the laser target is then aligned with the end of the previously laid section. The pipe section is maneuvered until the reference beam of light strikes the reference indicia on the target. Support material such as gravel, is then placed beneath the pipe section, holding it in place.
A continuing problem associated with prior art laser-based pipe alignment systems is the deflection of the laser beam caused by thermal stratification of the air in the pipe. As is well known in the art, the air in long pipe lines stratifies, with the warm air rising to the top of the pipe and the cooler air falling to the bottom of the pipe. This thermal stratification causes the laser beam to refract as a function of the temperature gradient within the pipe. During a construction project, many situations may occur which increase or decrease the temperature of the air in the pipe. For example, the pipe may experience thermal heating from the sun before being installed in the ground or the ambient air may be at a higher or lower temperature than the ground temperature.
The aforementioned refraction problems can be reduced or eliminated by increasing the air flow in the section of pipe. This enhanced air flow causes the air from various portions of the pipe to mix, resulting in more uniform temperatures within the pipe. Prior systems have used remote blowers to produce this air flow. One such blower 100 for increasing the air flow in a section of pipe 102 is shown in FIG. 1. A laser beam, generated by laser transmitter 106, establishes a reference beam of light 107. The blower 100 has a hose 108 and a output nozzle 110 attached thereto. During operation, a worker inserts the output nozzle 110 in one end of the pipe 102. The blower 100 thereafter forces air into the pipe 102 via the hose 108 and output nozzle 110 while the reference beam 107 travels through the pipe 102. The other end of the pipe 102 is aligned with the reference beam 107 using a laser beam target 112 having indicia thereon.
This system, although somewhat successful at reducing beam refraction, experiences less than adequate blower efficiency since the section of pipe is open at the output nozzle end. Thus, a substantial amount of the blown air exits the pipe at the blower end and fails to create air flow through the pipe. Furthermore, the pressure of the air flowing through the hose 108 drops significantly due to the relatively small diameter of the hose. This reduces the pressure of the air emerging from nozzle 110 and the resulting air flow through the pipe 102. The above described prior art system must use a relatively small diameter hose to allow transmission of the laser beam in the pipe concurrent with the generated air flow. Consequently, blower motors must be increased in size to compensate for the loss of air from the open end of the pipe and for the drops in air pressure in the hose.
In view of the shortcomings of the aforementioned prior art blower systems, there is a need for a pipe alignment device which produces air flow in a section of pipe in an efficient manner to reduce the deleterious effects of thermal stratification of the air in the pipe on a reference beam of light.